1. Field of the Invention
The present disclosure relates to a catalyst for preparing carbonate, and more particularly to a carbon nanomaterial-supported catalyst including phosphonium salt polymers.
2. Description of the Related Art
Catalysts play an important role in the chemical synthesis industry. Catalysts may improve reaction activity and shorten the reaction time, thereby reducing production costs. Catalysts can be generally divided into two major categories, homogeneous and heterogeneous catalysts. Although homogeneous catalysts have advantages of high activity and good selectivity, recovery is not easy, thereby increasing production costs. On the other hand, although heterogeneous catalysts are easily separated and recover easily, activity and selectivity thereof are not satisfactory.
In the chemical synthesis industry, cyclic carbonate ester is an important class of compounds in the field of an electrolyte for lithium batteries. The green process of cyclic carbonate ester involves using an appropriate catalyst for the cycloaddition reaction of carbon dioxide and epoxide. For example, a propylene carbonate, an important ingredient of an electrolyte in a lithium battery, can be obtained from the reaction of propylene oxide and carbon dioxide in the presence of catalysts.
In the resin industry, a non-isocyanate resin (NIPU) can be derived from a monomer with a cyclic carbonate functional group. Because the synthesis method avoids using highly toxic isocyanate esters, such as NIPU resin can be regarded as a “green” material. In addition, the low toxic nature allows the non-isocyanate polyurethane to be applied in biomedical materials. The green process of cyclic carbonate ester compounds uses carbon dioxides and epoxy compounds as raw materials. The cyclic carbonate ester compounds are obtained from the cycloaddition reaction of carbon dioxide with the epoxy group by using catalyst systems including a Lewis base, an ionic liquid, a metal complex, a heterogeneous metal salt, a silica-supported catalyst, a porous metal oxide salt, or an ion exchange resin. Among the catalysts mentioned above, salt or ionic liquid catalyst is most common. However, the existing homogeneous and heterogeneous catalyst systems have some shortcomings. For homogeneous catalysts, the catalysts and the products are homogeneous, and hence they are not easily separated and more purification procedure. For heterogeneous catalysts for reactions, the conversion rate of reactions is not satisfactory, and more harsh reaction conditions, such as higher gas pressure, are usually required for the catalytic reactions.
US Patent Publication No. 2005/070724A1 provides a zeolite-based catalyst for preparing cyclic carbonate. The heterogeneous catalyst serves as a Lewis base, and converts an epoxide into a cyclic carbonate in the presence of carbon dioxide. However, the reaction needs to be maintained under a high carbon dioxide gas pressure and more harsh reaction conditions (>6 atm, 120° C.).
U.S. Pat. No. 7,728,164 provides a phosphonium bromide salt (tetraalkylphosphonium bromide) as a homogeneous catalyst, which catalyzes the synthesis reaction of a propylene carbonate in the presence of carbon dioxide. The phosphonium bromide salt catalyst also requires more harsh reaction conditions. (>19 atm, 180° C.)
U.S. Pat. No. 6,933,394 provides a method of using phosphonium iodine salt compounds for catalyzing the reaction of epoxides with carbon dioxide to produce cyclic carbonate. The reaction with the homogeneous catalyst requires higher gas pressure (>100 atm), and has a higher demand for production equipment, thus increasing production costs.
Accordingly, what is needed in the art is a catalysis system having advantages of high catalytic reactivity as homogeneous catalysts and easy separation and recovery as heterogeneous catalysts.